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繧ケ繝ゥ繧、繝3(蠢懃畑:繝倥Μ繧ォ繝ォ驥代リ繝弱Ρ繧、繝、)

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(1)

Formation of helical

multishell gold nanowire

Theory :

Y. Iguchi, T. Hoshi and T. Fujiwara, PRL 99, 125507 (2007)

T. Hoshi and T. Fujiwara, JPCM21, 272201 (2009).

T. Hoshi, Y. Iguchi, and T. Fujiwara, Handbook of NanoPhysics 4,

Ed. D. Sattler, CRC Press, pp.36.1-18, (2010)(*)

ex. ‘11-4’-type nanowire

with L = 12 nm

section view (11-4 structure) Experiment :

Y. Kondo and K. Takayanagi, Science 289, 606 (2000)

(*) Preprint:

(2)

Formation of helical

multishell gold nanowire

Theory :

Y. Iguchi, T. Hoshi and T. Fujiwara, PRL 99, 125507 (2007)

T. Hoshi and T. Fujiwara, JPCM21, 272201 (2009).

T. Hoshi, Y. Iguchi, and T. Fujiwara, Handbook of NanoPhysics 4,

Ed. D. Sattler, CRC Press, pp.36.1-18, (2010)(*)

ex. ‘11-4’-type nanowire

with L = 12 nm

section view (11-4 structure) Experiment :

Y. Kondo and K. Takayanagi, Science 289, 606 (2000)

(*) Preprint:

http://www.damp.tottori-u.ac.jp/~hoshi/info/2010_Hoshi_AuNW_HNP_preprint.pdf

: 7-1, 11-4, 13-6, 14-7-1, 15-8-1 structures Specific shell configurations

with "magic number"

(3)
(4)
(5)

Geometrical theory for helical multishell gold nanowires

Initial non-helical structure in ideal FCC geometries

“Magic number” for specific multishell configuration

(1) no acute angle on the surface

(2) no (001)-like (square) side longer than any (111)-like (hexagonal) side

Rule for initial structural model

Add one atom row

10- 4

11- 4

6- 1

7- 1

[110] (001) (110) Relaxation

(6)

Two-stage formation model for helical structure

(1) Dissociation of the outermost shell from the inner shells (2) Slip deformation at the outermost shell

: from (001)-like (square) str. into (111)-like (hexagonal) str.

ex. 11-4 structure

B

(1)

(2)

(7)

Two-stage formation model for helical multishell gold nanowires

in various (experimentally observed) multishell configurations

(a) 7-1 (section view)

(b) 11-4

(c) 12-6-1

(d) 13-6-1

(e) 14-7-1

(f) 15-8-1

simulation steps

13-5-1

( 13-6 ?)

(8)

non-helical helical

Two-stage formation model for helical multishell gold nanowires

( Physical origin: wide 5d band )

non-helical

helical

Fig. expanded lateral surface (schematic)

(1) Dissociation of the surface (outermost) shell from the inner shells (2) Shear-like deformation at the surface shell

(9)

non-helical helical

Two-stage formation model for helical multishell gold nanowires

( Physical origin: wide 5d band )

non-helical

helical

Fig. expanded lateral surface (schematic)

What occurs

at domain bounary ?

[ Our short answer :

An atom pair is inserted ]

(1) Dissociation of the surface (outermost) shell from the inner shells (2) Shear-like deformation at the surface shell

(10)

Defect-induced helicity

by atom movement from inner shell

(11-4) type, (length) = 12 nm

Multiple helical domains

with different twisting directions A posible thinning process (?)

(11)

Relaxation simulation with longer nanowire (L=12 nm)

‘Green’ atom pairs are moved from the inner shell --> Helical domain boundary

Shear-like deformation on ‘red’ atoms : square --> hexagonal

oppsite shear directions

between left and right domains A B C C A D F D E

(12)

Relaxation simulation with longer nanowire (L=12 nm)

Initial

Final

‘Green’ atom pairs are moved from the inner shell --> Helical domain boundary

Red atoms: initially on the (001)-type

(square-lattice) surface area Green atoms: initially in the inner shell

Technical details ( Iguchi, Hoshi, Fujiwara, PRL99, 125507 (2007) )

Relaxation with thermal motion ( T = 600K, dt = 1fs ) Tight-binding Hamiltonian in the NRL form

Kirchhoff,et al. PRB63, 195101 (2001) da Silva et al. PRL 87, 256102 (2001).

Amorim and da Silva PRL 101, 125502 (2008)

Total energy [au]

(13)

Analysis : Why gold forms helical nanowire ?

‘Nanoscale competition’ beween

(a) Energy gain of helical transfomation on surface (’red’ atoms) (b) Energy loss of at domain boundary ( ’green’ atoms )

→ surface stabilization mechanism

simple energy scaling theory with domain length L

(a) ∆E

~O(L)

(b) ∆E

~O(1)

Energy [eV] Energy [eV]

final LDOS [ states/eV ] (a) (b) initial final initial

Physical origin : wide 5d band of gold (unlike 3d, 4d metals)

consistent to the features in reconstruction on equllibrium surfaces →

(14)

Change of the atom energy during the relaxation simulaiton

Iteration step Iteration step

Atom energy [eV]

P, Q : Atoms with energy gain (in surface reconstruction)

(15)

A simple energy-scaling theory with respect to domain length

Competitive feature of

(a) Energy gain of surface reconstruction (’red’ atoms) ( shear-like deformation : square --> hexagonal )

(b) Energy loss of defect fomation at domain boundary ( ’green’ atoms ) ( atom movement into wire surface)

= - 1.2 eV per unit layer

= + 2.4 eV at domain bounary

> 2 unit layers

(16)

Conclusion: Helical domain formation on multishell gold nanowire

Surface stabilization mechanism with > 2 unit layers (a) Energy gain of surface reconstruction

( shear-like deformation : square --> hexagonal ) (b) Energy loss of defect fomation at domain boundary ( atom pair supply into wire surface)

The same explanation holds on the equillibrium surfaces :

Reconstruction into (111)-like (hexagonal) strucutre on the Au(110) surface Possible physical origin : wide 5d band

DOS of FCC Cu, Ag, Au

(17)

‘Missing row’ structure in FCC(110) surface

→ (111)-type surface regions as successive nanofacets top

view

side view

(18)

Experiment: thinning process

of gold multishell nanowire

Y. Oshima, Y. Kondo, K. Takayanagi, J. Elec. Microsc. 52, 49-55 (2003)

in situ TEM images

Fig. expanded lateral surface (schematic)
Fig. expanded lateral surface (schematic)

参照

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